1. Field of the Invention
This invention relates to coated polypropylene films having improved heat seal strength, a higher level of coating to film adhesion and greater resistance to the deleterious effects of moisture, i.e., high humidity conditions, upon adhesion.
More particularly, it relates to such polypropylene films comprising polypropylene resins compounded with a minor amount of a maleated polyolefin resin and directly coated with a polyvinylidene chloride coating.
2. Description of the Prior Art
The introduction of oxygen in the form of carbonyl groups on the surface of polyolefin films has been widely used as a means of increasing the wetting and adhesion of coatings. In most cases, the oxygen concentration is increased by oxidation brought about by flame or corona discharge surface treatment. This adhesion enhancement is primarily due to the high electronegativity of the bonded oxygen atom and its tendency to promote hydrogen bonds with suitable proton donors present in the coating.
To our knowledge, maleated polyolefinic resins have never before been used (in combination) with isotactic polypropylene homopolymer resins as adhesion promoters for use with polyvinylidene chloride (PVDC) coatings.
The unique features of this invention in comparison to the present state of the art are as follows:
1. PVDC coated polypropylene film can be made that has a higher level of coating to film adhesion and a greater resistance to the deleterious effects of moisture upon adhesion. PA1 2. These additive systems, when compounded with polypropylene, improve coating to base film adhesion to the extent that one step coating is a practical method of application, hence the need for a primer is eliminated.